Methyl glucoside is a well-known industrial chemical which has been employed in the preparation of surfactants and as a plasticizer for various resins. Polyether polyols derived from methyl glucoside and other glucosides are particularly suitable as intermediates for the production of polyurethanes.
The preparation of methyl glucoside by the reaction of glucose with methanol in the presence of acid catalysts has long been known. U.S. Pat. No. 2,606,186 discloses the use of a cation exchange resin as a catalyst to replace the more typical mineral acid catalyst in the reaction. Typical resins employed were sulfonated-type cation exchangers including sulfonated phenolformaldehyde cation-exchange resins, sulfonated polystyrene cation-exchange resins, and sulfonated coal-type cation-exchange resins. It was necessary to isolate the product by crystallization in order to obtain material of suitable purity for use.
U.S. Pat. No. 3,928,318 discloses a modified method for preparation of methyl glucoside. In this disclosure, the procedure involved heating a mixture of glucose and methanol with sulfuric acid catalyst in the presence of a large amount of anhydrous calcium sulfate to remove water from the reaction mixture. A pressure vessel was also employed. Other commercial processes have used polysaccharides, such as starch, instead of glucose as the starting material.
Alkyl glucosides in general and methyl glucoside in particular are known to have poor alkali stability when they are produced on an industrial scale. This presents a problem when the glucosides are used for such applications as intermediates for the production of polyether polyols for polyurethane foams, since the reactions are carried out under alkaline conditions. The reaction of glucose with an alcohol, in particular methanol, in the presence of an acid catalyst according to known methods invariably yields a reaction product with poor stability in the presence of alkalis. This poor stability is caused by relatively high content of unconverted glucose and side-reaction products irrespective of whether a homogeneous or a heterogeneous acid catalyst is used. For this reason, industrial-grade methyl glucoside cannot be used directly for the most important applications. It must be subjected to troublesome, costly purifying and stabilizing treatment with bases or basic anion-exchange resins or by fractional crystallization.